//变量声明
#include <stdio.h>

int x;
int y;

int addTwo(){
    // 声明 x y 为外部变量
    extern int x;
    extern int y;

    x = 12;
    y = 6;

    return x-y;
}

int main(){
    int result = addTwo();
    printf("result = %d ", result);

}